When someone is walking beside you and they don't observe a straight line, but rather move into you in (unintentional) repeated, subtle bumps, much like a sheepdog herding cattle, forcing you off your intended path.

The sheepdogger is the one pushing; the sheepdoggee is the one getting pushed.

The act of getting a slow moving vehicle to drive faster by pulling up next to them and making them think you are going to cut them off. Usually done in traffic when there is not enough room to get passed the vehicle.

"Bro this car is moving so slow, and I can't get by because of all this traffic"
"Just sheep dog him, they will be compelled to drive faster"

The act of someone you are walking with failing to move laterally with you to allow you to pass obstacles. Instead, you are forced to slow down and follow them until you pass the obstacle, and then pick up the pace to catch up to your oblivious walking mate. You could also speed up to pass the obstacle first and let him/her catch up to you as well, but unfortunately this usually does not occur because you normally will have given your walking mate the benefit of the doubt prior, and up and to, the point of no return.

I had to walk about double the distance to the store as Dave because he kept sheep-dogging me.

Bar behaviour- A guy circles a group of women to scope them out, gradually 'herding' them into a smaller group. The ones who may not be interested naturally will move in closer to each other, leaving any stragglers on the edge of the herd vulnerable to the sheep-dogger...

I was sheep dogging this group of girls to see if there were any stragglers in the herd.